Atherosclerosis and its thrombotic complications are the leading cause of morbidity and mortality in developed countries. Non-invasive atherosclerotic plaque assessment using high-resolution magnetic resonance imaging (MRI) has been shown to be feasible in vivo in the human aorta, carotid, and coronary arteries. Flow suppression (i.e., black blood imaging) is necessary for vessel wall visibility and for preventing flow artifacts, which can affect image quality and interpretation. Black blood techniques include spatial presaturation (Nayak et al., Real-time black-blood MRI using spatial presaturation, J Magn Reson Imaging 2001;13:807-12) and double inversion recovery (DIR) preparation pulse modules (Simonetti et al., “Black-Blood” T2-weighted inversion recovery MR imaging of the heart, Radiology 1996;199:49-57).
The DIR preparation pulse modules typically consist of two 180-degree radio frequency (RF) pulses and are applied prior to image acquisition. The first non-selective RF pulse inverts the magnetization of the whole volume. The second selective RF pulse restores the magnetization in (“reinverts”) the slice of interest. After a time delay (inversion time, TI0), required for the magnetization of blood to reach the null point, the imaging slice is acquired (Simonetti et al.). The conventional DIR prepared two-dimensional imaging sequence acquires a few lines of k-space from one slice following each DIR module. Acquisition of multiple slices in this fashion results in long experiment times. For example, to acquire 20 slices with 256 lines and turbo factor of 9, a conventional DIR-RARE sequence would take 1160 RR intervals (the interval between two successive R waves of the heart), assuming triggering every other heart beat (repetition interval, TR, equal to two RR intervals). This DIR preparation in combination with a rapid acquisition with relaxation enhancement (RARE) readout has been successfully applied in vivo for vessel wall imaging of different vascular beds. Fayad et al., Clinical imaging of the high-risk or vulnerable atherosclerotic plaque, Circulation Research 2001;89:305-316. Yuan et al., Carotid Atherosclerotic Plaque: Noninvasive MR Characterization and Identification of Vulnerable Lesions, Radiology 2001; 221:285-99.
Improved DIR sequences to reduce examination time were recently developed. Song et al., Multislice double inversion pulse sequence for efficient black-blood MRI, Magn Reson Med 2002;47;616-20. Parker et al., Improved efficiency in double-inversion fast spin-echo imaging, Magn Reson Med, 2002;47:1017-1021. Yarnykh et al., Multislice double inversion-recovery black-blood imaging with simultaneous slice reinversion, J Magn Reson Imaging 2003;17:478-83.
Song et al. demonstrated a dual-slice DIR technique. The DIR preparation module was modified to include one non-selective and two slice-selective inversion pulses. Following the DIR preparation module, k-space lines from two slices were acquired. A single DIR preparation module was gated to each cardiac cycle (i.e., the repetition interval, TR, was equal to 1 RR interval). Song et al. suggested that data for additional slices could be acquired, but taught that the number of slices possible is limited by the time window during which blood magnetization is nullified. A later publication by Song et al. taught acquiring five slices after each DIR module, using a very short image acquisition sequence, and a DIR repetition interval equal to one RR interval. Song, Highly efficient double-inversion spiral technique for coronary vessel wall imaging, Proceedings of ISMRM 2002; 1566.
Parker et al. and Yamykh et al. taught that improved efficiency could be had by reducing the inversion interval (TI) for nulling the blood signal by administering a repetitive series of DIR modules (FIG. 1d) at a repetition interval short enough to put two DIR modules within each RR interval, but both publications taught that only a single slice of image data should be acquired after each DIR module. Parker et al. criticized the multislice technique proposed by Song et al. because “only one of the slices imaged will have the appropriate inversion time to null the signal from blood.”